Private-branch-exchange system



- Apr. 17,

M. L. NELSON PRIVATE BRANCH EXCHANGE SYSTEM 2 Sheets-Sheet l fnusnfuz"MEFZZZ'LL. EZE'C/Z'l Original Filed July 9 1917 Apr. 17, 1923.

M. L. NELSON PRIVATE BRANCH EXCHANGE SYSTEM 2 Sheets-Sheet 2[UL/517227.2- Z7.L.NEZ5UZ'L MEPZZ' Original Filed July 9 1917 Patentedl7, lhlildl MARTIN L. NELSON, OF CHICAGO, ILLIENOIS, .AiSSIGNOR TDAUTOMATIC? ELECTRIC COMPANY, 633 CHICAGO, ILLIHQIS, A GOB'POEATIUN OFILLINOIS.

PBIVATE BBANEEEEXCHANGE SEE'STEM.

Application filed July $3, 191?, Serial No. 179,327.

- themselves bymeans of automatic switching mechanisms, such an exchangeconstituting what is commonly known as a private automatic exchange, orP. .1 X. These exc ranges are usually installed in factories or businessestablishments of various kinds and, as in the GilllJOCliIl'lGllt hereindisclosed may consist f substations in each department and o'liice ofthe establishn'ient, and a switchboard comprising li or trunk selectingswitches individual to the lines and a suitieient number of connectorswitches to handle the maximum number of simultaneous calls. In aninstallation of this kind there are always a number f individuals, suchas a general foreman or superintendent, for ex ample having duties of asupervisory nature which often take them on inspection trips through thedifferent departments. Unless these trips are made in accordance with aregular schedule which. is seldom possible or even desirable, theseindividuals when so engaged will be bereft or telephone service so faras incoming calls are concerned. is true of course that an oiiicial bygoin to some trouble could notify his home station when he left for adifferent department and thus keep an attendant there posted as to hiswhereabouts but this plan would be inconvenient, and by my invention nosuch cumbersome arrangement is required.

llriefly stated the object of my invention is to provider. specialcoderinging andintercommunicating circuit whereby certain (licials may bereached when they are absent from their offices on business in otherdepartments. I provide a special bell in each department, all oi whichbells are connected in multiple across a common signaling circuit.Automatic code ringing" equipment is provided adapted to close thecommonsig' naling circuit in accordance with p: deter minedcodes, one ofwhich is assigned to each Renewed November 1?,1921. Serial No. 515,972.

fficial to whom special service is to be given. r tcertainset oicontacts-in the connector banks is to be used for the special signalingand thetelephone number associated therewith may be termed the specialcall nun her. it person who desires to commi iicate with an otlicial whois temporarily aliisent in some unknown department will call the specialcall number, thereby extending a connection to the code ringingequipment. One or more additional digits are now called in order to setthe ringing equip ment for the code ring ofthe particular 0 -ial wanted;whereupon'all the special bells are rung in parallel in a distinctivemanner which will be heardand'recognized by the desired party whereverhe happens to bc.' There is also a seccn'dset oi bank contacts set asidefor use in thiscounection', and upon perceiving: his signal the calledparty will turn to the nearesttelephone and a l the number correspondingto this second set of contacts, which 1 term the answer number; The twosets of bani: contacts are tied together s that by this operation thecalling; and called parties willbe telephonically connected.Conversation may be held overthecircuitthus established; or in caseanextended conversation is desired, one of the parties willgive theother his telephone number, which may be called in the usual w: thereby"freeing the code ringing'equip for use by someone else.

The foregoing; is a brief statement oi the object and scope of theinvention The preferred manner of carrying out the same, and theapparatus involved. will be described and explained fully hereinafter,reli'erence being had to the accompanying drawings, which show theessential features of a private automatic exchange embodying theprinciples of the invention.

- 1 shows diagxrammatically the circuits of two substations associatedwith two connectors in a manner to best illustrate my invention. I

2 shows diagrammatically a code A 7 ng equipment and the controllingcircuit therefor, arranged to function properly with circuit of Fi 1.

Referring to r, the substation A may be of any suitable automatic typesucln for enan l as the substation d' \losed in British parent to MartinNo. Z-zll9 of 1910. As shown herein itconsists essentially of a receiver2, the transmitter 3, switch hook 4, ringer 5, and condenser 6. Being anautomatic substation there is also provided a pair of impulse springs 7and 8 which are controllable by the impulse wheel 9 through the mediumof the finger hole dial (not shown).

The line conductors 121 and 13 terminate at the exchange in theindividual line switch C, which may be briefly described as a rotar lineswitch whose wipers have no norma position. A line switch of thischaracter is shown in the patent to Lamb, No. 1,193,160granted August 1,1916.

The'line switch C and a plurality of similar line switchesmay be givenaccess to a group of trunk lines, each of which extends to andterminates in a connector switch. One of the trunk lines to which theline switch C has access is shown in the drawing as terminating in theconnector E, which may be of the general type of connector shown inPatent No. 815,17 6, granted March 13, 1906 to Keith, Erickson andErickson. The side switch and private magnet are omitted, however, andthe circuits are modified in accordance with the two-wire system ofcontrol. These circuit changes, although forming no part of myinvention, will be explained fully hereafter during the description ofthe operation of the invention.

In the lower half of Fig. 1 .I have shown a substation A, an individualline switch C, and a connector E, which are in all respects similar tothe substation A and the switches C and E respectively.

It will be understood that the connectors E and E are two of a group ofconnectors which are used for the purpose of interconnecting calling andcalled lines in the usual manner. The banks of all the connectors of thegroup are, of course, connected in multiple and form terminals of normalconductors extending to the individual line switches associated with thelines of the system. This multipling of the banks is not shown in thedrawings, but is understood to be in accordance with the usual practice.In brief, the private automatic exchange in connection with which I havechosen to illustrate the invention, comprises a plurality of substationsincluding the substations A and A, a plurality of individual lineswitches, such as the line switches C and C, and a group of connectorsaccessible to all the line switches in common. A calling subscriber uponremoving his receiver operates his in dividual li'ne switch in order toselect and extend connection to an idle connector switch, and theselected connector is thereafter directively controlled to connect withthe normal conductors associated with a desired called line.

I It has been mentioned before that a certain set of contacts in theconnector banks is set aside for extending connection to the specialcode ringing equipment. While any set of contacts may be thus reserved,I prefer to use the last set in some particular level and in thefollowing it will be assumed that the last set of contacts in theseventh level is reserved for this purpose. The special call numbertherefore, will be the number 70. In this connection attention should becalled to the fact that each connector is provided with a set of specialrotary ofl normal springs which, in the case of the connector E, are thesprings 65, 66, and 67. The spring 67 is normally in engagement withspring and is adapted to be shifted into ei'igagement with spring 66 bythe rotary cam 7 5 when the connector is operated in accordance with thenumber 70. There'is also a set of contacts set aside for answering, tobe called when a party is responding to his code rin and it will beassumed that the contact set reserved for this purpose'is the ninth setof contacts in the seventh level. It

follows that the special answering number will be the number 7 9. Bothsets of contacts are multipled'as usual through the group of connectors.In addition the contact set corresponding to the call number 70 ismultipled with the contact set corresponding to the answering number 79. This is shown in the drawing as will now be pointed out. The contactset associated with connector E,

comprising bank contacts 93, 94, and 95, is

the last or tenth contact set in the seventh level, while the contactset associated with connector switch E is the ninth set of contacts inthe seventh level. The line contacts 93 and 95 are connected by means ofconductors 7 6 and 77 with line contacts 193 and 195. It will beobserved that these conductors are transposed so that the upper linecontact 98 is multipled with the lower line contact 195, while the lowerline contact 95 is multipled with the upper line contact 193. Theprivate or test contacts 94 and 194 are not multipled excepting, ofcourse, for the usual multiple to corresponding contacts in thedifferent connectors of the group.

From the test contacts 94 and 194 and the line contact 95, respectively,conductors 96, 97 and 98 extend to a group of relays which are indicatedcollectively by the reference character H, Fig. 2. These relays have thefunction of controlling the rotary switches M and N in a manner whichwill be described fully hereinafter. The rotary switch M may be termed acode selecting switch and comprises essentially a stepping magnet 113and the four wipers 115 to 118, inclusive,

with their associated sets of bank contacts.

The switch M may be similar in construction to the rotaryline switch C,Fig. 1, although, of course, the circuits are altogether differentbecause of the different operations which the switch has to perform. TherolOO menses tary switch N is similar to the rotary switch M but hasonly two wipers 119 and 120. The stepping magnet for the switch N isindicated by the numeral 111. The switch N may be termed a ringingswitch and its function is to close the common signaling circuit inaccordance with the code selected by the switch M. This circuit isclosed over the conductor 121 which extends to the relay 122. Whenenergized the relay 122 connects the generator Genoss the conductors 123and 124; which extend to all the offices or departments of the businessestablishment in which the system is installed. As before explained, asignaling device or ringer is connected across these conductors in everydepartment. Three oi these ringers are shown in the drawings and areindicated by the reference characters R, It, and R The bank wiringbetween the switches M and N will notbe explained in detail just now,but will be described in the course of the description of the operationWhile I have shown throughout the drawings a plurality of batteries itwill be understood that there is preferably but one battery having itspositive pole grounded. In order not to encumber the dr; wings separaterei erence characters have not been applied to the separate batteries,but it will be understood that when, in the description of theoperation, a circuit is traced to battery it extends to the live orui'igrounded pole of central battery. The busy signaling machine Q andthe intermittent ringing equipment I R shown in Fig. 1 are of the usualtype common in other well known automatic e2;- changes.

I-laving given a brief description of the apparatus involved, I will nowproceeo to describe more in detail the operation of? the system. Forthis purpose it will be assumed that the subscriber substation L. i

i n new desires to communicate with an oflicial X who is known to betemporarily absent from his oflice. Usually the subscriber at substationwill have ascertained this fact by calling X at his office in the usualmanner. However, this is of no importance for it is sufficient forpresent purposes to assume that X is at some unknown point in theestablishment and that in order to communicate with him it will benecessary to use the special call system provided by my invention. Thesubscriber at substation A will theretore remove his receiver andoperate his calling device in accordance with the digits oi the callnumber 70.

Upon removal of the receiver a circuit is completed for the line relayof the line switch C as follows: ground at 1. resting contact ofarmature 1S and said armature. line conductor 13, substation A lineconductor 12, armature and its resting contact, and the winding of linerelay lfi to the closeof the above circuit, the line relay connects theprivate or test wiper 31 to the junction point 24 as follows: test wiper31, armature 19 and its resting contact, armature 22 and its workingcontact, to junction point 2 1. It is understood that the wipers of theline switch are normally in engagement with some contact set in the bankand the operation now depends upon whether the contact set upon wiichthe wipers are resting is busy or not. If this contact set is busy thetest contact which is engaged by the test wiper 31 will have a groundpotential upon it, resulting in the energization of the stepping magnet.17 and the short circuiting ot' the relay 16. By the operation of thestepping magnet 17 the switch wipers are advanced to the next contactset, and since the stepping magnet interrupts its own circuit, theadvance of the wipers will be continued through the vibratory operationof the stepping magnet as long as the test wiper 311 continues to engagegrounded or busy test contacts. When an idle or ungrounded test contactis reached, which we will assume to be the test contact 34. theoperation of the stepping magnet will cease, and the relay 16, being nolonger short circuited, will be energized over the previously describedcircuit extending from ground G The resistance of relay 16 issuiiiciently high to prevent the stepping magnet 17 from energizing overthis circuit.

By the operation of the relay 16 the test wiper is connected to thewinding of the said relay at its armature .19; and at armatures 20 and18 the line conductors 1.2 and 13 are disconnected, respectively. fromthe winding of the line relay 15 and from ground G. and are extended byway of line wipers and 32 and bank contacts 33 and to the windings ofthe double wound line relay of the connector E.

The line relay 10 is accordingly energized in the usual manner over thecalling subscribers loop. and completes the usual circuit for the slowacting release. relay 41. Upon attracting its armatures relay s1prepares the usual circuit for the vertical and rotary magnets 48 and4-9 (at lower armature 52) and at its upper armature 78 closes a holdingcircuit for the relay 16 of line switch G which may be tracedas follows:ground at G working contact of armature T2 and the said armature. banlcontact 3%, test wiper 31. armature 19 audits working contact, windingof relay 16, and winding of magnet 17 to battery. 11. branch of theabove circuit extends from junction point till by way of private normalconductor 27 to multiple test contacts in the banks of the connectorswhere, by a, ground potential on these test contacts, the line ofsubstation A is made busy.

The foregoing operations have occurred automatically in response to theremoval of the receiver at substation A- The calling subscriber may nowoperate his calling device in accordance with the first digit of thecall number which is the digit 7. lVhen the calling device is operatedthe impulse springs "i" and 8 are separated momentarily seven times,producing a corresponding series of interruptions in the circuit of theline relay of the connector E. In response to these interruptions of itscircuit the line relay 40 is deenergized a number of times and at eachdeenergization transmits an impulse to the vertical magnet 48 over thefollowing path: ground at G armature 51 and its resting contact,armature 52 and its working con tact. off normal springs 59 and 58,winding of the low resistance slow acting relay 42, and the winding ofthe vertical magnet 48 to battery. In response to these impulses thevertical magnet is operated to raise the switch shaft step by step untilthe wipers 90, 91, and 92 stand opposite the seventh horizontal level ofbank contacts. The slow acting relay 42 is energized in series with thevertical magnet and retains its armature attracted during the series ofimpulses, thereby preventing the opening of the vertical magnet circuitat the off normal springs which are shifted as soon as the switch shaftleaves its normal position.

The calling subscriber may now call the final digit of the special callnumber, which is the digit 0. As before, by momentary separations of theimpulse springs 7 and 8, a series of interruptions is produced in thecircuit of the line relay 40. Now, however, the off normal springs beingin the position shown in the drawing, and the relay 42 havingdeenergized, the line relay transmits a series of impulses to the rotarymagnet 49, the circuit being as follows: ground at G armature 51 and itsresting contact, armature 52 and its working contact, oif normal springs59 and 57, armature 53 and its resting contact, winding of lowresistance slow acting relay 45, resting contact of armature 72 and thesame armature, armature 54 and its resting contact, and the winding ofthe rotary magnet 49 to battery. The rotary magnet is operated inresponse to these impulses to rotate the switch shaft until the wipers90,91, and 92 are brought to rest in engagement, respectively, with bankcontacts 93, 94, and 95, which bank contacts comprise the tenth set ofcontacts in the seventh level. The slow acting relay is energized inseries with the rotary magnet 49 and maintains its armatures continuallyattracted during the rotation of the switch. At its lower armature 60relay 45 disconnects the test wiper 91 from thelower winding of relay 46and connects it instead by way of spring 70, resistance 47, and theresting contact of armature 60 and said armature, to the upper windingof the combined test and answering bridge relay 43. The momentarycnergizations of relay 43 due to the test wiper 91 passing over busy orgrounded test contacts, if there be any such in its path, are of noconsequence because of the alternative circuit for the rotary magnet byway of armature 68 of relay 45 and its working contact. The connectorwipers having been rotated into engagement with the set of bank contactscorresponding to the special call number, the operation now depends uponwhether the special code ringing equipment associated with that set ofcon tacts is busy or not. In order to explain the operation of theconnector E in calling a busy line, it will first be assumed that thespecial ringing equipment is busy. Under these circumstances, there willbe a ground potential on the test contact 94 and when the connectorwipers are rotated into engagement with bank contacts 93, 94, and 95,relay 45 being energized during the rotation as before described, assoon as the test wiper 91 arrives at the test contact 94 the relay 43will be energized over tne circuit previously traced with the followingresults: At the resting contact of armature a contact in the circuit ofthe lower winding of relay 46 is opened and at the working contact ofthe same armature relay 43 prepares a locking circuit for itself whichis completed upon the deenergization of relay 45 an instant later, andwhich extends as follows: ground at G working contact of armature 78 andthe said armature, conductor 79, armature 55 and its working contact,contact point 71, spring 70, resistance 47, resting contact of armatureand said armature, and the upper winding of the said relay 43 tobattery. In addition, the circuit of the rotary magnet 49 is opened atthe resting contact of armature 54 and at the working contact ofarmature 56, a lead from the busy signaling machine Q, is connected tothe lower heavy line conductor in order to notify the calling subscriberthat the attempted connection cannot be obtained. He will accordinglyreplace his receiver, whereupon the automatic switches C and E arerestored to normal condition in a manner which will be hereinafterdescribed.

Having explained briefly how the connector E operated when a busy lineis called, I will now return to where it was explained how in responsetothe final series of impulses the switch wipers were rotated on to thebank contact set corresponding to the call number 70, and from thispoint the regular operation will be proceeded with. If there is noground potential upon the test contact 01, when the slow acting relay 15deenergizes at. the end of the final series 01? impulses the followingenergizing circuit is completed for the switching relay ground at Gworking contact o1 armature 78 and the said armature, condrwtor '70,armature 553 and its resting contact, lower winding of relay 16, restingcontact 01 arnia ture 09 and the said armature, test wiper 01., testcontact as, conductor 96, armature 105 and its resting contact, and thewinding 01? relay 102 to battery. Upon the closure of r the abovecircuit relays 16 and 102 are energized in series. As a result of theenergization of the former relay at resting contact of armature T2 thecircuit of the rotary magnet 419 is opened, and at the workingcontact ofthe same armature a circuit is prepared tor the ring cut off relay 414.As a further result of its energization, relay 4E6 closes a contact inthe lower heavy talking conductor at its armature 74:, and at itsarmature 73 short circuits its lower winding and completes a lockingcircuit for itself by way oi? its upper winding, the circuit beingtraceable as follows: ground at G working contact; of armature 78 andthe said armature, conductor 79, armature 73 and its two workingcontacts to the upper winding of the said relay 16 and to the test wiper91. By the connection of direct ground to the test contact 9 1 and itsmultiples, the special ringing equipment is made busy in the banks oithe remaining connectors of the group. The operation of relay 102, Fig.2, which it will be remembered was energized in series with the relay4:6 01 the connector, is without particular function just at this time.

The connection. has now been extended to the trunk line terminating inthe special ringing equipment shown in Fig. 2, and the apparatus is inreadiness for the transmis sion of setting impulses to code selector M.The calling subscriber is, of course, acquainted with the code ringwhich has been assigned. to the wanted party X, and knows, also, whatdigit is now necessary to be called in order to operate the codeselector 1W1 for the purpose of selecting this particular code ring. -Wewill assume that the code ring used tor signaling X is one long and oneshort. and that thecode selector M is so wired that in order to selectthis particular code ring, the digit five must be called. The callingsubscriber will, therefore, operate his calling device in accordancewith this digit, thereby producing as before, a series 0t interruptionsin the line circuit and a corresponding series of deenergizations of theline relay 10. These deenergizations of the line relay are at this timeineffectual to cause any Further operation of the connector E for therotary magnet circuit has been opened,

as before explained, at the resting contact of the armature It has beenexplainedbetore, however, that when the connector E is operated. inaccordance with the number the rotary 011' normal springs 65, 66, and 67are shifted, and since these springs, therefore, will now be in theposition shown in the drawing, the deenergizations of the line relay nowresult in the transmission of a series of impulses to the steppingmagnet 113 of the code selectorM, the circuit being as follows: ground(i armature 51 and its resting contact, armature 52 and its workingcontact, oft normal springs 59 and 57, armature 53 and its restingcontact, rotary oft normal springs 66 and 67, resting contact ofarmature 63 and the said armature, armature 7 1 and its working contact,wiper 92, hank contact 95, conductor 98, armature 106 and its restingcontact, armature 108 and its resting contact, winding o1 low resistanceslow acting relay 103, and the winding of the stepping magnet 113 tobattery. Five impulses are transmitted to the stepping magnet 113 overthe above circuit and the switch wipers 115 to 118, inclusive. whichnormally rest in engagement with the first contacts in their respectivebanks, are advanced live steps to the position shown in the drawing.Relay 103 is energized in series with the stepping magnet 113 and beingslow acting retains its armature during the series of impulses. At theend of the series of impulses relay 103 deenergizes and connects groundG to the Wiper 115, thereby closing an energizing circuit for the relay101 as tollows: ground G, resting contact of armature .111 and the saidarmature, wiper 115 and the ban; contact engaged thereby, conductor 131, and the winding of relay 101 to battery. Upon energizing, relay 101prepares a circuit tor the relay 100 at its arma-- ture 107 and at itsarmature 108 opens the circuit of the stepping magnet 1113. A branch ofthe energizing circuit of relay 101 may be traced to relay 104: asfollows: junction oint 136, armature 110 and its working contact,interrupter contact otthe steppi g magnet 114 of ringing switch N. andthe winding of the stepping relay 104: to

battery. Upon energizing, relay 1041 completes an extension of the abovetraced branch as follows: junction point 137, ar-

mature 112 and its working contact, and the winding of stepping magnet114 to battery.

The stepping magnet 1141 is accordingly energized and by its operationthe wipers 119 and 120 of the ringing switch N are advanced one step.Near the end of its stroke the magnet 1141 opens the circuit of thestepping relay 10 1 which is thereupon deenergized and opens the circuitof the stepping magnet. A vibratory action is thus set up between thestepping relay 104: and the stepping magnet 11-1, whereby the wipers 119and 120 are advanced step by step into engagement with successivecontacts in their respective banks, and it will be evident that thisoperation will continue as long as a ground potential is maintained uponthe junction point 137.

hen on its second step the wiper 120 arrives at the contact 140 acircuit is completed for the relay 122 as follows: ground at G, restingcontact of armature 111 and the said armature, wiper 115 and the bankcontact engaged thereby, conductor 133, wiper 120, bank contact 140,conductor 121, and the winding of the said relay 122 to a battery. Uponenergizing, relay 122 bridges the generator Gren across the twoconductors 123 and 124, thereby operating the ringers R, R R and allother ringers similarly connected. When the wiper 120 reaches contact141 on the third step the circuit of the relay 122 isnot interrupted,but is maintained closed over the following path: grounded wiper 120 byway of bank contact 141, conductor 125, bank contact engaged by theWiper 118 and the said wiper, conductor 132, conductor 121, and windingof relay 122 to battery. Obviously, the above circuit will continue tobe closed while the wiper 120 is passing bank contact 142. During thetime that the wiper 120 is in engagement with the contact 143 thecircuit of re lay 122 is closed over the path originally described.While the wiper 120 is in engagement with contacts 144 and 145 thecircuit of relay 122 is still maintained closed over the following path:grounded wiper 120, contact 144 or 145, conductor 126, contact engagedby the wiper 117 and the-said wiper, conductor 132, conductor 121, andthe line relay 122 to battery. It will be evident, also, that While thewiper 120 is in engagement with bank contact 146, the circuit will stillbe closed as originally. Thus it will be seen that the circuit of therelay 122 will be closed continuously while the wiper 120 is passingcontacts 140 to 146, inclusive, thereby producing a long closure of thecommon signaling circuit. But while the wiper 120 is passing contacts147 and 148 the circuit of the relay 122 is interrupted, for it will beseen when tracing the circuit that none of the contacts to which theconductor 127 is multipled in the bank of the code selector M is engagedat this time by the wiper 116. The relay 122 is accordingly deenergizedwhile the wiper 120 is passing contacts 147 and 148. When the contact149 is reached the circuit of the relay 122 is again completed asoriginally described, and since the circuit is interrupted again uponthe arrival of wiper 120 at contacts 150 and 151 the relay 122 isenergized only momentarily to produce a short closure of the signalingcircuit. As the wiper 120 continues its rotation and successlvelyengages the remaining cont/ads in its bank, it produces no furtheroperations of the relay 122, as may be readily ascertained by tracingthe circuit connections of the remaining contacts. After completing onerevolution the wipers of the switch N immediately start on another, andit follows that the signaling operation just described will be repeatedat intervals.

When the called party X hears one of the special bells ringing inaccordance with his code he will step to the nearest telephone, which wewill assume to be the substation A, and call the answering number 79.Upon the removal of the receiver at the substation A the line switch Cis operated automatically the same as was described in connection withthe line switch C to select and establish connection with a trunk lineextending to an idle connector switch. Assuming that the selectedconnector isthe connector E, when the calling device at substa tion A isoperated in accordance with the digits of the number 79, the connector Ewill be operated under control of its line relay 180 to raise and rotateits wipers 190, 191, and 192, until they come to rest in engagement withthe bank contacts 193, 194, and 195, respectively. The connector Eoperates precisely like the connector E, and therefore the manner inwhich the above connection is established will not be described indetail. WVhen the slow acting relay 186 deenergizes at the end of therotation, a circuit is completed for the switching relay 185 as follows:ground at G, working contact of armature 181 and the said armature,conductor 182, armature 183 and its resting contact, lower winding ofrelay 185, resting contact of armature 179 and the said armature,

test wiper 191, test contact 194, conductor 97, and the winding of relay100 to battery. Relays 185 and 100 are energized in series on theclosure of the above circuit and the en ergization of the former relayhas the usual results among which may be mentioned the preparation of anenergizing circuit for the ring out 01f relay 187 at armature 178, andthe grounding of test wiper 191, and the closure of a locking circuitthrough the upper winding of the said relay 185 at armature 184. Thelower line wiper 192 is also connected at the working contact ofarmature 177, whereby an energizing circuit is completed for the ringcut off relay 44 of connector E as follows: ground at G or G, .dependingon the position of the intermittent ringing equipment I R, generator Genor the booster battery, conductor 176, rotary off normal springs 175 and174, resting contact of armature 173 and the said armature, armature 177and its working contact, wiper 192, bank contact 195, conductor 77, bankcontact 93, wiper 90, lower wind ing of the ring cut off relay 44,working con-- tact of armature 72 and the said armature,

iii)

armature and its resting contact, and the winding oi the rotary magnet19 to battery. Upon the closure of the above circuit the ring cut oilrelay is energize-ll. the rot magnet 49 remaining inoperative, r:armature 61 completes a loosing itself as tollows: ground atG workingcontact ot armature '78 and the said armature. conductor 79, armature S1l its we contact, and the upper windi oi the said relay t-lto battery.As a in ier result oi its energization relay extends the app 1' andlower heavy talking conductor oy or its armatiu-es 60 and 63 through tothe line wipers QOand 92, respectively. An energizing circuit for thering cut oil relay 187 of the connector E may nowbe traced over thefollowing path: groundat G working contact armature 78 and the saidarmature, conductor 79, armature 61 and its working contact, lowerwinding of relay a3, spring 62, armature armature 7-1.- and its workingcontact, wiper 92, bani: contact- 95, conductor 76, bank contact 193,wiper 190, lower winding ot ring cut'ott relay 187, working contact ctarmature 178 and the said. armature, armature 172 and its restingcontact, and the winding of the rotary net 171 to battery. Current flowin the above circuit brings about the energization o1 relay 187 withresults similar to those de scribed in the case of the ring cut oilrelay 14 of connector ll including the extension of the heavy talkingconductors by way of armaeurcs 188 and 173 to the wipers 190 and 192.The complete talking circuit between the substations A and A has nowbeen established The transmitters at the two substations are suppliedwith talking cur-- rent through the windingso'l the line relays ll) and180, respectively, while the voice currents take the path shownin theheavy lines. The back bridge relays i and 170 which supply talkingcurrent to the called subscribers in ordinary connections will evidentlybe' energized in series, but have no battery supplying function in aconnection of this character. It will be seen that the automaticoperation of the ring cut oh relays in the two connectors is due tothctransposition of the conductors76 and 77 which'has been beforementioned, and it may be stated that these conductors are reversedespecially for this purpose.

lie-turning to the re ay Hit), Fig. .2, which, it will be recalled, wascnei.'.fize(l in SONGS 1th the relay 185 of connector E, the operationof this relay opens the circuit of the stepping magnet 11 at a newpoint, (armature .106), and also serves to lisconnect the CODClUCiZOI"96 u the winding of relay 102 and connect it instead direct to ground atthe working contact of :11 ature 105. l" 102 does not deener eize once,however, hut is held'up tempo'arilyfover the lay 41-1.

following circuit ground at G, resting con tact of armature 111, wiper115 and the eon-- tact engaged thereby, conductor 183, wiper 119 of therotary switch it and the contact engaged thereby, conductor 138, and thewinding oi relay 102 to battery. As soon 'as the switch N completes itsrevolution the above circuit will be broken, for the first contact ofthebank associated with wiper 119 is not in multiple with the remainingcontacts. Relay 102 is therefore deenergized with the following results:At the rest ing contact of armature 110 a circuit is completed for thestepping magnet 11?) for the purpose of restoring the code selectingswitchM to normal position, and at the resting contact of armature 109an auxiliary energizing circuit is completed for the relay 100 in orderto maintain this relay energized and the contact sets 70 and 79 busy incase the subscribers should hang up their receivers before the codeselector M had reached its normal position. The circuit oi the steppingmagnet 113 mentioned above may be traced as follows: ground at G",resting contact of arn'lature 111 and the same armature, wiper 115' andcontacts engaged. thereby, conductor 13%, armature 110 and its restingcontact, interrupter contact of the stepping magnet 113, and winding ofsaid magnet to battery. Since the above. circuit includes theinterrupter contact of the stepping magnet, the said magnet willoperateintermittently to advance the switch wipers step by step to complete therevolus tion, the operation of the stepping magnet ceasing only when thewiper 1.15 arrives at the first/contact in its bank. When this hasoccurred the circuit of the stepping mag; net has been opened. in anobvious manner, and also the circuit of rela 101. this relay beingrleenergized to open the above mentioned auxiliary energizing circuitfor relay 100. p

Referring to the talking conncmion which has been established throughthe medium 0? the apparatus shown in Fig. 1, when a con versationisfinished both parties will replace their receivers. At the replacementof the receiver at substation A the circuit of the line relay is brokenresulting in the do eoergization oi the line relay and also in thedeenergi ntion of the slow acting release re- By this operation thecircuit of the release magnet closed as follows: ground at G armature 51and its resting contact, armature and its resting contact, lower oftnormal springs, and the winding of said release magnet 50 to battery.The operation of the release magnet is effective to restore theconnector to normal position in the usual manner, its circuit beingbroken by the off normal springs when the switch shaft reaches itslowest position. As a furtl'ier result ot the deenergiaation of therelease relay'41 ground G is disconnected from the holding circuitextending back to the relay 16 of the individual line switch (I Belay 16accordingly deenergizes to restore the circuit of the line switch to itsnormal condition. The connector E and line switch C are released in thesame manner a result of the replacement of the receiver at thesubstation A. All or the apparatus involved in the connection has nowbeen restored to normal in readiness for other words In View of thepreceding explanation it is believed that the operation of the codeselector M and the ringing switch N insignaling in accordance with theother codes will be understood without goin any further into details.While a variety of wiring schemes may be used for selecting the variouscode rings, the one which has been worked out is comparatively simpleand is appended below in the form of a table for the benefit of thosewho may wish to practice the invention:

ga S1gnal code.

701 l 1 long 702 2 long 703 4 short 704 5 short 705 1 long and 1 short706 1 short and 1 long 707 1 long and 2 short 708 1 long and 3 short 4709 1 long, 1 short and 1 long 7001 2 short and 1 long 7002 3 short and1 long 7003 1 short, 1 long and 1 short 7004 1 short, 1 long and 2 short7 7005 2 short, 1 long and 1 short 7006 1 short and 2 long 7007 2 longand 1 short 7008 1 long and 4 short 7009 4 short and 1 long 70001 3short, 1 long and 1 short 70002 2 short, 1 long and 2 short 70003 1short, 1 long and 3 short 70004 6 short It will be observed that certainof the call numbers appearing in the above table require the calling ofeither two or three digits instead of one in order to control the set ofthe code selector M. To provide for this, the 11th and 21st contacts inthe bank associated with the wiper 115 are not mul tipled with theremaining contacts so that when the code selector is operated inaccordance with the digit 0, for example, when the slow acting relay 103deenergizes at the end of the series of impulses, the rin ing switch I?will not begin its operation It the next'digit called is some digitother than 0 the end or the series of impulses the ringing switch N willbe started as pre viously described for all contacts between the 11th21st are multipled with the ones preceding the 11th. If the next digitcalled is again 0, however, the wiper 115 will be advanced to the 21stcontact, making it necessary to call still another digit before theringing operation will begin. The switch is prevented from stopping onthe 11th and 21st contacts during the release by means of a conductor13-5 which serves when relay 102 is deenergized to join these twocontacts to'the remaining ones.

Having described my invention, what I consider to be new and desireto'have pro tected by Letters Patent will be pointed out in the appendedclaims:

What I claim as my invention is:

1. In a telephone system, a pair of con nected terminals common to theexchange, means, whereby a calling subscriber can obtain a connectionwith the first of said termi nals, other terminals multiplied to saidfirst terminals, and means for making said terminals busy when saidcalling subscriber obtains connection with said first terminal,signaling means associated with said first terminals for signaling acalled subscriber, and means whereby the called subscriber can obtain aconnection with the second of said terminals while said other terminalsare busy, whereby the said calling and called subscribers may betelephonically connected.

2. In a telephone system, a pair of connected terminals common to theexchange, telephone call and answer numbers assigned to said terminalsrespectively, means operated in accordance with the call number forconnecting a calling subscriber with one of said terminals and formaking said terminal busy when said calling subscriber obtainsconnection thereto, means for signaling the called subscriber, and meansoperated in accordance with the answering number for connecting thecalled subscriber with the other of said terminals while said firstterminal is bus, whereby said subscribers may be telephonicallyconnected.

3. In a telephone system, a pair 01 connected terminals common to theexchange, telephone call and answer numbers assigned to said terminals,respectively, means operated in accordance with the call number forconnecting a calling subscriber with one of said terminals and formaking said terminal busy when said calling subscriber obtainsconnection thereto, means for signaling the called subscriber inaccordance with a predetermined code, and means operated in accordancewith the answering number for connecting the called subscriber with theand other or said terminals while said first terminal is busy, wherebysaid subscribers may be telephonically connected.

a l. In a telephone system, a pair of connected terminals common to theexchange, automatic switching mechanism controlled by ii-callingsubscriber for establishiiu; connection with the first oiisaid terminalsother terminals multipled to said first terminals, and means for makingsaid terminals busy when said calling subscriber obtains connection withsaid first terminal, signaling means associated with said first terminaltor signaling a called subscriber, and automatic switching mechanisnrcontrolled by the called subscriber tor establisl'iinp a connection withthe second oil said terminals while said other terminals are busy,whereby the said calling and called subscribers may be telephonicallyconnected.

In a telephonesystem, a pair of connected terminals common to theexchange, telephone call andanswer numbers assigned to said terminals,respectively, automatic switching mechanisn'i controllal'ile by acalling subscriber in accordance with the call number for extending aconnection to'one of said terminals and for malting said terminal busywhen said calling subscriber obtains connection thereto, means for thensignaling the called subscriber, and automatic switching mechanismcontrolled by the latter in accordance with the answering number torextending a connection to the other of said terminals while said firstterminal is busy, whereby the calling and called subscribers may betelephonically connected.

(5. In a telephone system, a pair of connected terminals common to theexchange, telephone call and answer numbers assigned to said terminals,respectively, automatic switching mechanism controllable by a cal in;-subscriber in accordance with the call number for extending a connectionto one of said terminals and "tor making said terminal busy whensaid'calling subscriber obtains connection thereto, a common signalingsystem and means tor operatingthe same in accordance with apredetermined code to signal a called subscriber, and automaticswitching mechanism controlled by the latter in. accm'dance withtheanswering number tor extending a coi'incction to the other o'i' saidterminals while said first terminal is busy, whereby the calling and'called subscribers may be telephonically connected.

7. In a private branch exchange system, a plurality of special signalslocated at. ditferent points in the system. a common circuit foractuating allsa-id signals simultaneously in order to notify a party atsome unknown point thathe is wanted, means for bringing said circuitunder the control of the calling subscriber, means controlled by thesubscriber for determiniag rhe code by which said signals are to beoperated, and automatic means for thereafter causing said. signal to beactuated in accordance with the predetermined code.

8. In a private branch exchange system, a plurality of special signalslocated at difterent points in the system, a common circuit toractuating all said signals simultaneously in order to notify a party at.some unknown point that he is wanted, means under control or" thecalling subscriber for controlling said circuit in a predetermineddistinctive manner to signal the particular party wanted and automaticmeans for thereafter actuating said signals in said predeterminedn'ianner.

9.In a private branclnexchange system, a plurality of special signalslocated atdit l erent points in the system, a common circuit toractuating all. said signals simultaneously in order to notify a party atsome unknown point that lie wanted; means controlled by the callingparty tor preparing a talking circuit, and for thereafter closing saidsignaling circuit, and means controlled by the called party in responseto the signal for con'ipleting said talking circuit and for opening saidsignaling circuit.

10. In a private branch exchange systemi a plurality of special signalslocated at ditterent points in the system, a common cir cuit toractuating all said signals simultaneously in order to notify a party atsome unknown point that he is wanted, a code selector switch and. acontrolling switcl'i, means under control of the calling party forsetting said code selector to signal the particular party wanted, andcircuit connections whereby said controlling switch is operated automatically thereafter to close said signalingcircuit in accordance withthe selected code.

11. In a private branch. exchange f *steni. a common signaling circuitcomprising); a plurality oi signaling devices, equipment comprising acode selector and a controllinir switch, automaticswitching mechanismcontrolled by a calling, subscriber in. accord ancewith the digits of aspecial call number for extendingv a connection to said equipment. andmeans i-m- "then settingsaid code selector in accordance with anotherdin'it. the said controlling switch being automati cally responsive tothe setting ot said code selector for closing said signaling circuitinaccordance with the selected code.

1.2. The method of connecting callina' and called sul'iscribers inconversation in an ai'itoniatic te ephone syst .n. which consists oi theoperation of an automatic switch by a calling; subscriber to connectwith one of a pair of terminals accessible to the subscriber andstarting the operationofa code signalling equipment associated therewithto signal the called "suscriber, and in thejfope ation as auto n;

switches by the called party in response to the signal to connect withthe other of said pair of terminals and thereby automatically stop theoperation of said code signaling: equipment and complete the connectionbe-- tween the calling and called subscribers.

13. In a telephone system, a pair of connected terminals common to theexchange, means whereby a calling subscriber can obtain a connectionwith the first of said terminals, signalling means associated with thefirst of said terminals for signalling a called subscriber, meanswhereby the called subscriber can obtain a connection with the second ofsaid terminals whereby the calling and called subscribers may betelephonically connected, and automatic means responsive to theestablishment of said telephonic connection for disconnecting saidsignalling means.

14. In a telephone system, a pair of connected terminals common to theexchange, telephone call and answer numbers assigned to said terminals,respectively, means operated in accordance with the call number forconnecting a calling subscriber with one of said terminals, means forsignalling the called subscriber in accordance with a predeterminedcode, means operated in accordance with the answering number for connecting the called subscriber with the other of said terminals whereby saidsubscri jiers may be telephonically connected, and automatic meansresponsive to the establishment oi" 5? said telephonic connection fordisconnecting said signalling means.

15. In a telephone system, a pair of connected terminals common to theexchange,

automatic switching mechanism controlled by a calling subscriber forestablishing a connection with the first of said terminals. signallingmeans associated with said first terminals for signalling the calledsubscriber, automatic switching mechanism controlled by the calledsubscriber for establishing a connection with the second of saidterminals, whereby the said. calling and called subscribers may betelephonically connected. and automatic means responsive to theestablishment of said telephonic connection for disconnecting saidsignalling means.

16. In a telephone system, telephone lines, a pair of connectedterminals common to the exchange, automatic switching mechanismcontrolled from a calling one of said lines for establishing connectionwith the first of said. terminals, code signalling means associated withsaid first terminals. an auto-- matic switch associated with. said firstter-- minals, means controlled from said calling line for operating saidautomatic switch to select a particular code in order to signal rsubscriberat an unknown point in the exchange, and automaticswitchingmechanism controlled by the'said called subscriber forestablishing a connection with the second of said terminals, wherebysaid calling and called subscribers may be telephonically connected.

17. In a telephone system, telephone lines, a pair of connectedterminals common to the exchange, automatic switching mechanismcontrolled from a calling one of said lines for establishing connectionwith the first of said terminals, code signalling means associated withsaid first terminals, an automatic switch associated with said firstterminals, means. controlled from said calling line for operating saidautomatic switch to select a particular code, signals common to theexchange, means for operating said common signals in accordance with theselected code to signal a subscriber at an unknown point in theexchange, and means controlled by the said called subscriber forestablishing a connection with the second of said terminals whereby saidcalling and called subscribers may be telephonically connected.

18. In a telephone system, a pair of connected terminals common totheexchange, automatic switching mechanism controlled by a callingsubscriber for establishing connection with the first of said terminals,code signalling means associated with said first set of terminals, meanscontrolled by said calling subscriber for selecting a particu lar code,a plurality of signals common to the exchange, automatic means foractuating said signals in accordance with the selected code to signal acalled subscriber, and automatic switching mechanism controlled by thesaid called subscriber for connecting with the second terminals, wherebysaid calling and called subscribers are telephonically connected.

19. In a telephone system, a pair of connected terminals common to theexchange, automatic switching mechanism controlled by a callingsubscriber for establishing connection with the first of said terminals,code signalling current associated with said first terminals, a codeselecting switch accessible from said first set of terminals, meancontrolled b'y said calling subscriber for operating said code selectingswitch to select a particular code, signalling devices common to theexchange, automatic means for actuat- 111g said. devices'in accordancewith the selected code, and means controlled by a called subscriber forobtaining connection with the other set of terminals therebyestablishing a telephonic connection with said calling subscriber 20. Ina telephone system, a pair of con-- nected terminals common to theexchange, automatic switching mechanism controlled by a callingsubscriber for establishing connection with the first of said terminals,code signalling current associated with said first terminals, a codeselecting switch accessible iling devices.

n a telephone system, a pair of connected terminals common to theexchange,

automatic switching mechanism controlled by a chilling subscribertorestabhshing connection with the first of said terminals, codesignalling current associated with said first terminals, a codeselecting switch accessible from said first set of tern'1inals, meanscon trolled by said calling subscriber for operating said code selectingswitch to select a particular code, signalling devices common to theexchange, automatic means for actuating said devices in accordance withthe selected code, means controlled by a called subscriber for obtainingconnection with the other set of terminals thereby establishing trolledb said callin subscriber tor onerating said code selecting switch toselect a particular code, signalling devices common to the exchange,automatic means for actuatin; said devices in accordance with theselected code, means controlled by it called subscriber for obtainingconnection with the other set oi terminals thereby establishing atelephonic connection with said calling subscriber, and automatic meansresponsive to the establishment or said telephonic connection forreleasing said code selector.

23, In a telephone system, two sets of con nected terminals common tothe exchange, automatic switching mechanism controlled by a callingsubscriber for extending a connection to one of said sets oi terminals,a source of code signalling current, a code selector accessible fromsaid first set of terminals, means controlled by the said callingsubscriber for operating said code selector to select a particularcode,signalling devices common to the exchange, automatic means for operatingsaid signalling devices in response to the selected code to signal acalled subscriber, automatic switching mechanism controlled by thecalled subscriber for extending a connection to said second set ofterminals whereby the calling and called subscribers are telephonicallyconnected, and automatic means responsive to the establishment of thelast connection for releasing said code selecting switch.

24. In. a code ringing machine, a pair of step bystep switches,permanent conductors connecting the bank contacts of onevswitch with thebank contacts of the other, ringing mechanism, subscriber controlledmeans for operating one of said switches to select a desired code, andautomatic means for operating the other of said switches to operate saidringing mechanism in accordance with the selected code.

25. In a telephone system, a signalling circuit, a plurality of signalsconnected to said circuit, a code selecting switch operable by a callingsubscriber to select a code,

mechanism cooperating with said switch for operating said signals oversaid circuit according to the code selected, and means for preventingthe restoration of said switch and cooperating mechanism in case thecalling subscriber hangs up his receiver before the code is finished,

26. In a telephone system, a signalling circuit, a plurality of signalsconnected to said circuit, a code selecting switch operable by a callingsubscriber to select a code, mechanism cooperating with said switch foroperating said signals over said circuit according to the code selected,means for restoring said switch and cooperating mechanism controlled bythe calling subscriber, and means for preventing the calling subscriberfrom producing a false signal by restoring said switch and cooperatingmech- 'anism before the code is completed.

27. In a telephone. system, a signalling circuit, a plurality of signalsconnected to said circuit, a code selecting switch operable by a callingsubscriber to selecta code, mechanism cooperating with said switch foroperating. said signals over said circuit according to the codeselected, means controlled by a called subscriber for stopping thesignalling operation. and means for preventing the stopping of. thesignalling operation before the code is finished.

28. In a telephone system, a signalling circuit, a plurality of signalsconnected to said circuit, a code selecting switch operable by a callingsubscriber to select a code, a sending switch cooperating with saidselecting switch to operate said signals over said circuit in accordancewith'the code selected, an operating circuit for said sending switchinitially closed by the calling subscriber, and locking means forpreventing the opening of said circuit until the code is completed.

29. In. a telephone system, a signalling circuit, a plurality of signalsconnected to said circuit, a code selecting switch operable by a callingsubscriber to select a code, a

sending switch cooperating with said selecting switch to operate saidsignals over said circuit in accordance with the code selected,

subscriber controlled means for restoring said selecting switch, andmeans for preventing the restoration of said selecting switch while saidsending switch is in an oil normal position.

50. In a telephone system, a signalliugcircuit, a plurality of signalsconnected to said circuit, a code selecting switch operable by acallingsubscriber to select a code, asending switch cooperating with saidselecting switch to operate said signals over said circuit in accordancewith the code selected, means controlled by the called subscriber forstopping the signalling operation, and means for preventing the stoppingof the signalling operation while said sendingswitch is in an off normalposition.

31. In a telephone system, asignalling circuit, a plurality of signalsconnected to said circuit, a code selecting switch operable by a callingsubscriber to select a code, a send- 111g switch cooperating with saidselecting I switch to operate said signals over said cir- 7 normalposition.

33. Inc code ringing machine, a register switch adapted to be set inaccordance with a code digit, a" rotary switch for transmitting thecode, means for operating; said Totary switch continuously to repeat thecode at intervals, and means for preventing the restoration oi saidregister switch. ex-

cept when the said rotary switch is in a particular position.

34;. In a telephone system, a pair of terminal sets common to theexchange, unlike call and answer numbers assigned to said sets,respectively, automatic switching mechnism controlled by a callingsubscriber in accordance with the call number for connect ing with thefirst of said sets, automatic switching mechanism controlled by thecalled subscriber in accordance with the answer number for connectingwith the second of said sets, and conductors connecting said terminalsets to permit conversation between said subscribers.

35. In atelephone system, a plurality of automatic switches, a set ofmultiply connected calling terminals in each 0i said switches having acall number, a set of multiply connected answering terminals in each ofsaid switches having an answer number,

means under the control of a calling subscriber -for operating one ofsaid switches in accordance with the call number to connect with a setof calling terminals, means under the control'ot the called subscriberfor operating another of said switches in accordance with the answernumber to connect with a set of answering terminal-sand multipleconnections between the calling and answering terminal sets to permitconversation between said subscribers.

36. In a telephone system, a pair of terminal sets common to theexchange, an automatic connector switch operable by a calling subscriberfor connecting with the first of said terminal sets, a second automaticconnector switch operable by the called subscriber for connecting withthe second of said terminal. sets, a back bridge relay in each connectorbridged across the wipers thereof in series with the exchange battery,and transposed conductors connecting said terminal sets whereby saidrelays are energized in series.

37. The combination, with a register switch adapted to be set inaccordance with a digit in a number, of a code sending switch, automaticoperating means for said second switch, and conductors connecting bankcontacts of said register switch with bank contact-s of said sendingswitch, whereby the code sent out is in accordance with the setting ofsaid register switch.

Signed by me at Chicago, Cook County, Illinois, this second day of July,1917.

MARTIN L. NELSON.

